328 



SCIENCE 



[N. S. Vol. XLI. No. 1052 



published in Italy in the course of the last 

 fifty years," by Mario Vecchi ; " Mathematical 

 methods in physics " (review of Volterra's Sur 

 quelques Progres reeents de la Physique mathe- 

 matique, Drei Vorlesungen iiber neuere Fort- 

 schritte der mathematischen Physik, and 

 Leeons sur I'Integration des Equations aux 

 Derivees partielles), by J. B. Shaw; Shorter 

 notices : Berkeley's Mysticism in Mathematics, 

 by C. J. Keyser; Aubert and Papelier's Exer- 

 ciees de Geometrie analytique, by F. M. Mor- 

 gan; Hardy's Orders of Infinity, by W. A. 

 Hurwitz; Smith and Karpinski's Hindu- 

 Arabic Numerals, by J. V. McKelvey; Dal- 

 wigk's Darstellende Geometrie, by J. V. Mc- 

 Kelvey; Schmid's Darstellende Geometrie, by 

 Virgil Snyder; Auerbach's Graphische Dar- 

 stellung, by Virgil Snyder ; Meyer's Differ- 

 ential- und Integralrechnung, by Virgil 

 Snyder ; Note on " The discovery of inversion," 

 by Arnold Emeh ; Correction ; " Notes " ; and 

 " New Publications." 



SPECIAL ARTICLES 



THE IDENTITY OF HELIOTEOPISM IN ANIMALS AND 



PLANTS. SECOND NOTE ^ 



Paul Bert had shown in 1869 that if the 

 small fresh-water crustacean Daphnia is ex- 

 posed to a solar spectrum it goes towards the 

 source of light in all parts of the visible spec- 

 trum, but most rapidly in the yellow or green. 



II fut facile de remarquer qu'elles aecouraient 

 beaucoup plus rapidement au jaune ou au vert 

 qu'a toute autre eouleur.2 



The fact of the predominance of the helio- 

 tropic efficiency of the yellowish-green in these 

 and some other animals led the ophthalmol- 

 ogist Hess to two assumptions, first that they 

 are totally color-blind (since the yellowish- 

 green part of the spectrum is the brightest for 

 the eye of the totally color-blind human) and 

 second, that the sensation of brightness is the 

 cause of the heliotropic reaction of animals. 

 It is obvious that these conclusions go beyond 

 the facts, since we have no proof for the as- 

 sumption that the heliotropic effects of light 

 in lower animals are accompanied or deter- 



^ Loeb and Wasteneys, Froc. Nat. Acad. Sc, I., 

 p. 44, 1915. 



2 Paul Bert, Arch, de Physiol, II., p. 547, 1869. 



mined by any sensations of brightness and 

 since totally color-blind humans do not show 

 any positive heliotropism. In consequence of 

 his two arbitrary assumptions, Hess is forced 

 to the further conclusion that the heliotropic 

 reactions in animals and plants can not be 

 identical, since he does not seem ready to dis- 

 cuss the light and color sensations of plants, 

 and he tries to support this conclusion by the 

 statement that heliotropic plants and animals 

 are sensitive to different parts of the spectrum, 

 all animals to the yellowish-green, all plants 

 to the blue. We have already pointed out in 

 our previous note^ that this latter statement is 

 not correct, since we were able to show that for 

 the positively heliotropic animal, Eudendrium, 

 the most efficient part of the spectrum lies in 

 a carbon arc spectrum in the blue near the 

 region A = 474 jx/ji, where it also lies, according 

 to Blaauw, for the seedlings of oats. 



It seemed of interest to find out whether for 

 different motile unicellular organisms which 

 contain chlorophyll and which are on the 

 border line between plants and animals the 

 most efficient part of the spectrum for the 

 production of heliotropic reaction lies always 

 in the same region. We investigated the re- 

 actions of Chlamydomonas pisiformis and of 

 Euglena viridis in a carbon arc spectrum. 

 The investigation of the behavior of these 

 organisms in the spectrum showed a marked 

 difference. Euglena gather in the blue part 

 of the spectrum, usually in the region between 

 A=-438 and A^510ya/x. The densest gather- 

 ing was generally in the region of A ^=' 475 fjcfi,. 

 In the case of Chlamydomonas the gathering 

 always went much farther towards the yellow, 

 usually having its limit in the region of about 

 A ^560 or A = 570/x/x. It was in most cases 

 not easy, however, to ascertain the region of 

 maximal gathering, though in many cases it 

 seemed to be about A =■ 520 ix/jl. The most re- 

 markable difference between the behavior of 

 the two forms in the spectrum was therefore 

 the fact that Chlamydomonas was sensitive to 

 longer waves than Euglena. 



It soon became obvious that this method of 

 procedure does not permit the decision of the 



3 Loeb and Wasteneys, Proc. Nat. Acad. Sc, I., 

 p. 44, 1915. 



